From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f48.google.com (mail-pb0-f48.google.com [209.85.160.48]) by kanga.kvack.org (Postfix) with ESMTP id B6D416B0035 for ; Fri, 25 Apr 2014 04:28:42 -0400 (EDT) Received: by mail-pb0-f48.google.com with SMTP id md12so2940008pbc.7 for ; Fri, 25 Apr 2014 01:28:42 -0700 (PDT) Received: from lgeamrelo04.lge.com (lgeamrelo04.lge.com. [156.147.1.127]) by mx.google.com with ESMTP id pn4si4306588pac.298.2014.04.25.01.28.40 for ; Fri, 25 Apr 2014 01:28:41 -0700 (PDT) Date: Fri, 25 Apr 2014 17:29:41 +0900 From: Joonsoo Kim Subject: Re: [PATCH 2/2] mm/compaction: cleanup isolate_freepages() Message-ID: <20140425082941.GA11428@js1304-P5Q-DELUXE> References: <20140421124146.c8beacf0d58aafff2085a461@linux-foundation.org> <535590FC.10607@suse.cz> <20140421235319.GD7178@bbox> <53560D3F.2030002@suse.cz> <20140422065224.GE24292@bbox> <53566BEA.2060808@suse.cz> <20140423025806.GA11184@js1304-P5Q-DELUXE> <53576C08.2080003@suse.cz> <5357CEB2.1070900@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5357CEB2.1070900@suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka Cc: Minchan Kim , Andrew Morton , Mel Gorman , Heesub Shin , LKML , Linux Memory Management List , Dongjun Shin , Sunghwan Yun , Bartlomiej Zolnierkiewicz , Michal Nazarewicz , Naoya Horiguchi , Christoph Lameter , Rik van Riel On Wed, Apr 23, 2014 at 04:31:14PM +0200, Vlastimil Babka wrote: > >>> > >>> Hello, > >>> > >>> How about doing more clean-up at this time? > >>> > >>> What I did is that taking end_pfn out of the loop and consider zone > >>> boundary once. After then, we just subtract pageblock_nr_pages on > >>> every iteration. With this change, we can remove local variable, z_end_pfn. > >>> Another things I did are removing max() operation and un-needed > >>> assignment to isolate variable. > >>> > >>> Thanks. > >>> > >>> --------->8------------ > >>> diff --git a/mm/compaction.c b/mm/compaction.c > >>> index 1c992dc..95a506d 100644 > >>> --- a/mm/compaction.c > >>> +++ b/mm/compaction.c > >>> @@ -671,10 +671,10 @@ static void isolate_freepages(struct zone *zone, > >>> struct compact_control *cc) > >>> { > >>> struct page *page; > >>> - unsigned long pfn; /* scanning cursor */ > >>> + unsigned long pfn; /* start of scanning window */ > >>> + unsigned long end_pfn; /* end of scanning window */ > >>> unsigned long low_pfn; /* lowest pfn scanner is able to scan */ > >>> unsigned long next_free_pfn; /* start pfn for scaning at next round */ > >>> - unsigned long z_end_pfn; /* zone's end pfn */ > >>> int nr_freepages = cc->nr_freepages; > >>> struct list_head *freelist = &cc->freepages; > >>> > >>> @@ -688,15 +688,16 @@ static void isolate_freepages(struct zone *zone, > >>> * is using. > >>> */ > >>> pfn = cc->free_pfn & ~(pageblock_nr_pages-1); > >>> - low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages); > >>> > >>> /* > >>> - * Seed the value for max(next_free_pfn, pfn) updates. If no pages are > >>> - * isolated, the pfn < low_pfn check will kick in. > >>> + * Take care when isolating in last pageblock of a zone which > >>> + * ends in the middle of a pageblock. > >>> */ > >>> - next_free_pfn = 0; > >>> + end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn(zone)); > >>> + low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages); > >>> > >>> - z_end_pfn = zone_end_pfn(zone); > >>> + /* If no pages are isolated, the pfn < low_pfn check will kick in. */ > >>> + next_free_pfn = 0; > >>> > >>> /* > >>> * Isolate free pages until enough are available to migrate the > >>> @@ -704,9 +705,8 @@ static void isolate_freepages(struct zone *zone, > >>> * and free page scanners meet or enough free pages are isolated. > >>> */ > >>> for (; pfn >= low_pfn && cc->nr_migratepages > nr_freepages; > >>> - pfn -= pageblock_nr_pages) { > >>> + pfn -= pageblock_nr_pages, end_pfn -= pageblock_nr_pages) { > >> > >> If zone_end_pfn was in the middle of a pageblock, then your end_pfn will > >> always be in the middle of a pageblock and you will not scan half of all > >> pageblocks. > >> > > > > Okay. I think a way to fix it. > > By assigning pfn(start of scanning window) to > > end_pfn(end of scanning window) for the next loop, we can solve the problem > > you mentioned. How about below? > > > > - pfn -= pageblock_nr_pages, end_pfn -= pageblock_nr_pages) { > > + end_pfn = pfn, pfn -= pageblock_nr_pages) { > > Hm that's perhaps a bit subtle but it would work. > Maybe better names for pfn and end_pfn would be block_start_pfn and > block_end_pfn. And in those comments, s/scanning window/current pageblock/. > And please don't move the low_pfn assignment like you did. The comment > above the original location explains it, the comment above the new > location doesn't. It's use in the loop is also related to 'pfn', not > 'end_pfn'. Okay. Following patch solves all your concerns. End result looks so nice to me. :) Thanks. --------->8----------------